There is no "official" record for the fastest softball pitch. Here are some of the reputed records after a search of various archives:
Guinness is supposed to have clocked a softball pitch at 68.9 miles per hour.
National Pro Fastpitch (NPF), a women's professional softball league, claims that pitches of "70+" MPH are common. There are many other references in various sources making the same 70+ miles per hour claim.
The fastest softball pitch reportedly clocked at the Atlanta Olympics was 73.2 MPH.
Eddie Feigner, a famous softball player and the founder of the "King and His Court" 4-man softball team is supposed to have been clocked at 104 miles per hour. In a game against Major Leaguers ballplayers, Eddie Feigner struck out, Willie Mays, Roberto Clemente, Brooks Robinson Willie McCovey, Maurey Wills, and Harmon Killebrew all in a row.